x86/irq/64: Use cpu entry area instead of orig_ist

The orig_ist[] array is a shadow copy of the IST array in the TSS. The
reason why it exists is that older kernels used two TSS variants with
different pointers into the debug stack. orig_ist[] contains the real
starting points.

There is no point anymore to do so because the same information can be
retrieved using the base address of the cpu entry area mapping and the
offsets of the various exception stacks.

No functional change. Preparation for removing orig_ist.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Borislav Petkov <bp@suse.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Nicolai Stange <nstange@suse.de>
Cc: Sean Christopherson <sean.j.christopherson@intel.com>
Cc: x86-ml <x86@kernel.org>
Link: https://lkml.kernel.org/r/20190414160144.885741626@linutronix.de

arch/x86/kernel/irq_64.c

@@ -18,6 +18,8 @@
 #include <linux/uaccess.h>
 #include <linux/smp.h>
 #include <linux/sched/task_stack.h>
+
+#include <asm/cpu_entry_area.h>
 #include <asm/io_apic.h>
 #include <asm/apic.h>
 
@@ -43,10 +45,9 @@ static inline void stack_overflow_check(struct pt_regs *regs)
 {
 #ifdef CONFIG_DEBUG_STACKOVERFLOW
 #define STACK_MARGIN	128
-	struct orig_ist *oist;
-	u64 irq_stack_top, irq_stack_bottom;
-	u64 estack_top, estack_bottom;
+	u64 irq_stack_top, irq_stack_bottom, estack_top, estack_bottom;
 	u64 curbase = (u64)task_stack_page(current);
+	struct cea_exception_stacks *estacks;
 
 	if (user_mode(regs))
 		return;
@@ -60,9 +61,9 @@ static inline void stack_overflow_check(struct pt_regs *regs)
 	if (regs->sp >= irq_stack_bottom && regs->sp <= irq_stack_top)
 		return;
 
-	oist = this_cpu_ptr(&orig_ist);
-	estack_top = (u64)oist->ist[ESTACK_DB];
-	estack_bottom = estack_top - DEBUG_STKSZ + STACK_MARGIN;
+	estacks = __this_cpu_read(cea_exception_stacks);
+	estack_top = CEA_ESTACK_TOP(estacks, DB);
+	estack_bottom = CEA_ESTACK_BOT(estacks, DB) + STACK_MARGIN;
 	if (regs->sp >= estack_bottom && regs->sp <= estack_top)
 		return;